Repeated daily exposures of rhesus monkey eyes by an operant conditioning technique to spectral lights 2 to 3 log units less intense than the threshold intensity for gross burn damage produce loss of blue cone response after blue light exposure lasting longer than three years and of green cone response after green light exposure lasting between 18 and 45 days. Red light exposures within 10 percent of the gross burn threshold produce only 24 hour effects. Retinal sections of the eyes of the "blue-blinded" monkeys show swollen pigment epithelium and cone damage which ranges from swelling of mitochondria and axonal processes to total degeneration. In comparing the exposed with the unexposed eyes, there also appear to be cones completely missing in vertical 1 micron thick retinal sections in the parafoveal region. A new technique in our laboratory, using a histochemical marker in conjunction with spectral light exposure, has succeeded in labeling the complete color-receptor mosaic of the goldfish and is now underway successfully on the primate. It is proposed to continue this research with: (a) continued parametric studies of wavelength-intensity-duration relationships for producing the effect using goldfish and rhesus monkeys; (b) continued histological study using light and electron microscopy to attempt to identify the primary lesion in photic damage; (c) application of the histochemical technique to obtaining firm evidence on which retinal elements are involved as a function of wavelength and energy of exposure.